Electrostatic gas filters

ABSTRACT

An electrostatic gas filter element for use in a gas filter includes three substantially planar electrodes spaced in substantially parallel planes along the direction of the gas flow. Each electrode includes a metallic frame across which are strung either lengths of braided wire or helical springs. The center electrode receives a first voltage while the two outer electrodes a different voltage.

United States Patent [191 Schwab 5] June 18, 1974 1 ELECTROSTATIC GAS FILTERS [76] Inventor: Louis Schwab, PO. Box 76, Fern Park, Fla. 32730 [22] Filed: Mar. 21, 1972 [21] Appl. No.: 236,638

[52] U.S. C1 55/123, 55/136, 55/139, 1 55/146, 55/147, 55/148, 55/151 [51] Int. Cl. B03c 3/02 [58] Field of Search 55/105, 123, 124, 126, 55/130,131,136,137,138,139,150,151,

[56] References Cited UNITED STATES PATENTS 945,917 1/1910 Cottrell 55/2 1,329,237 l/1020 Frisbie 55/128 1,794,615 3/1931 HOSS 55/136 2,016,531 10/1935 Wintermute. 55/136 2,049,561 8/1936 Grave 55/123 X 2,251,451 8/1941 Heinrich.. 55/139 X 2,440,455 4/1948 White 55/139 X 2,579,441 12/1951 Palmer 55/138 X 2,637,408 5/1953 Yadoff 55/139 X 2,640,559 6/1953 Hills 55/139 X 2,650,672 9/1953 Barr et a1 55/139 X 2,708,488 5/1955 Larsson 55/151 2,852,093 9/1958 Streuber 55/147 X 2,987,137 6/1961 Brixius et al 55/138 3,040,497 6/1962 Schwab v 55/123 3,054,245 9/1962 Aron 55/139 X 3,724,174 4/1973 Walkenhorst... 55/D1G. 35 3,739,552 6/1973 Webster 55/154 X FCREIGN PATENTS OR APPLICATIQNS 421,151 11/1925 Germany 1. 55/136 657,376 3/1938 Germany 55/139 Primary ExaminerDennis E. Talbert, Jr. Attorney, Agent, or Firm-1-1ane, lBaxley & Spiecens ABSTRACT An electrostatic gas filter element for use in a gas filter includes three substantially planar electrodes spaced in substantially parallel planes along the direction of the gas flow. Each electrode includes a metallic frame across which are strung either lengths of braided wire or helical springs. The center electrode receives a first voltage while the two outer electrodes a different voltage.

5 Claims, 9 Drawing Figures FIRST VOLTAGE SOURCE 22' secouo VOLTAGE sourzce 24 PATENTEBJuu 1 a an FIRST VOLTAGE SOURCE Z2 SECOND VOLTAGE SOURCE 24 SHkU 1 OF 2 FIG.

FIG. 4'

FIG. 3

ELECTROSTATIC GAS FILTERS Thisinvention pertains to electrostatic gas filters and more particularly to improvements in my US. Pat. No. 3,040,497.

Although filters made according to the above cited patent perform well they have created a demand for even better filters. Inparticular, the use of two elec trodes, one receivinga DC voltage andthe other receiving an RF. voltage, limits the rate of agglomeration of particles and the separation of parasites since there is a limit to how varied one can make the gradients of the electrostatic fields. Further, the electrodes of the filter elements are. complicated structures usingrelatively expensive smooth rods to minimize arcing and similar effects.

It is, therefore, an object of the invention to provide an improved electrostatic gas filter element for generating much more complex electrostatic fields which have more complex voltage gradients to enhance agglomeration of sub-micron particles.

It is another object of the invention to provide such filter elements with electrodes which are not only less expensive than previously usedelectrodes butwhich at the same time aid in the generationof those voltage gradients which enhance agglomeration of the submicron particles.

These and other objects are accomplished by an electrostatic gas filter element which is to be positioned in a gas stream. The filter element comprises first, second and third electrode means which are aligned in substantially parallel and spaced relationship withthe second electrode means located between the first and third electrode means. Means apply a firstvarying voltage to the first and third electrode means; andlother means apply a second and different varying voltage tothe second electrode means to create very diverse field gradients to enhanceparticle agglomeration. The invention further contemplates new and unusual electrode means which both simplify fabrication of the filter element and increase the efficiency operation of the. filters.

Other objects, features and advantages of the invention will be apparent from the following detailed description whenread with" the accompanying drawings which show, by way of example, andnot limitation apparatus embodying. the invention.

In the drawing:

FIG. 1 is a perspective view of a gas filter according to the invention shown schematically positioned in a duct confining a gas stream;

FIG. 2 is a sectional view through the electrostatic gas filter element of the gas filter of FIG. 1 to show the staggering of the conductors of the electrode means;

FIG. 3 is a frontelevation of one embodiment of the electrode means of FIGS. 1 and 2;

FIG. 4 is a front elevation of another embodiment of the electrode means of FIGS. 1 and 2;

FIG. 5 shows a portion of the conductors used in=the embodiments of FIGS. 3 and 4;

FIG. 6 is a front elevationof a further embodiment of the electrode means of FIGS. 1 and 2; and

FIGS. 7, Sand 9 are waveforms of the voltages generated by the voltage sources of FIG. 1.

In FIG. 1 an electrostatic gas filter element 10 is shown positioned in aduct 12 (indicated schematically by dashedlines) through which a gas such as air containing pollutants flows in the direction of arrow 14.

In general, upstream from electrostatic. gas filter element. 10 there is acollector element (not shown) which mechanically, by a screeningaction, removes the particle pollutants. However, becauseof the mesh sizesused in such collector elements,.many of the sub-micron sized particles are nottrapped. Accordingly, the electrostatic gas-filter element. l0is used to agglomerate first, second and third electrode. means 16,. 18, 20'

aligned in, preferably 2-inch, spaced planes perpendicular to the direction of gas flow. The outer electrode means 16 and 20 are connected to a first voltagesource 22', and the central electrode means 18 is connected to a second voltage source 24. Since all the electrode means are the same, only typicalelectrode means 16 will be described in detail.

Electrode means 16 comprises a rectangular frame 26 of conductive material across which extend a plurality of, preferably 2-inch, spaced parallel conductors 28. As can be seen in FIG. 2, the conductorsof each electrode means areoffset from those of its neighbor to enhance gas flow.

In one embodimentof the electrode means 16, a portion of which is shown in FIG. 3,.tlie frame includes two spaced and parallel bars 30and32ofconductive material. Each bar carries aplurality of. regularly spaced conductor engagingmeans in the form of eyelets 34. The conductors 28 are formedfrom asingle length of wire hereinafter more fully described. The wire is laced through the eyelets in a regular pattern to provide a plurality of parallel conductors which extendbetween the bars 30 and 32.

In an alternate embodiment of the electrode means l6"shown in FIG. 4, the frame also includes a pair of spacedand parallelbars 40 and 42 of conductive material. Fitted on each bar is a plurality of tubular spacers 44. The spacers 44 are disposedin aregularly spaced arrangement. The conductors 28 are again fonned from a single length of wire. The wire is wound around.

one bar at the interspacer gap then tothe other bar where itis wound around the bar at another interspacer gap in a regular pattern to provide a plurality of parallel conductors which extendacross the frame.

In both of the embodiments of FIGS. 3 and 4, not only is easy fabricationobtained but also complex elec tric field gradient properties are obtained by using braided wire such as the shielding of microphone cable as shown in FIG. 5. In fact, it has been found that the irregular surface of such wire and particularly the diamond-shapedbraided surface gives an irregular field.

FIG. 6shows another embodiment of the electrode means 16" which has similar properties, includes a frame with two spaced bars 60 and 62 of conductive material, each provided witha plurality of regularly spaced kinks 64. The conductors are now metal springs 66. The ends of each spring have hooks 68. and for engaging kinks 64lof the bars 60 and 62.

As was stated above, the electrode meansreceive energizing voltages fromsources 22 and 24.

First voltage source 22 generates a high amplitude (tens of kilovolt) low frequency (kilohertz) voltage having a generally sawtooth waveform. Again, to enhance the irregularity of the field gradients, the trailing edge'of the waveform has an AC. ripple. The voltage can swing from ground in the positive direction as shown in FIG. 7, or in the negative direction, or swing above and below ground as shown in FIG. 8. Second voltage source 24 can generate the same voltage as source 22, but of opposite polarity. Or, the voltage can be a low amplitude (hundreds of volts) high frequency (hundreds of kilohertz) voltage having a sinusoidal waveform. Such voltage generators are well known, per se, in the art and accordingly, will not be described. For example, a voltage generator for generating waves of the type shown in FIG. 7 is set forth in U.S. Pat. No. 3,040,497. For example, a voltage generator for generating waves of the type shown in FIG. 9 (the wave form supplied by the second voltage source 24) is set forth in Paragraph 66: Multitube Transmitter Circuits, C-W and A-M RECEIVERS, Department Of The Army Technical Manual TM 1 1-665, Sept. 1952, pages 103-108.

By using such voltages and such conductors, completely irregular electric fields are generated in the region of electrostatic gas filter 10. Since the charges and the masses of the pollutants varies over a broad range, such irregular fields increase the likelihood of accelerating the pollutants and enhance agglomeration and the Q separation of the parasites from their particles making for less odor and smoke.

While the invention has been described in detail with respect to certain now preferred examples and embodiments of the invention, it will be understood by those skilled in the art, after understanding the invention, that various changes and modifications may be made without departing from the spirit and scope of the invention, and it is intended, therefore, to cover all such changes and modifications in the appended claims.

What is claimed is:

1. An electrostatic gas filter element to be positioned upstream of a collector element comprising: a duct; three planar electrode means in said duct, said electrode means being perpendicular to the axis from said duct and spaced from each other, whereby a first electrode means is disposed between the other two electrode means, each of said electrode means comprising a frame including two spaced and parallel bars of conducting material, and a length of braided multi-wire metallic conductor connected to said parallel bars to form an array of parallel conductors extending between said bars, the parallel conductors of said first electrode means being positioned with respect to the parallel conductors of at least one other of the planar electrode means so as to be mutually offset with respect to the axis of said duct; means for applying a first voltage which sinusoidally varies about ground potential to said said first electrode means; and means for applying a second pulsating voltage which is unidirectional with respect to ground potential with a portion of its waveform having an AC. ripple to both of said other two electrode means.

2. The electrostatic gas filter element of claim 1 wherein each of said two spaced and parallel bars carry a plurality of spacers and said length of multiwire metallic conductor is alternately and regularly wrapped in gaps between said spacers and extending across the space between said bars.

3. The electrostatic gas filter element of claim 1 wherein said second voltage has an amplitude in the kilovolt range.

4. The electrostatic gas filter element of claim I wherein the wires of said metallic conductor are braided according to a diamond pattern.

5. An electrostatic gas filter element to be positioned upstream of a collector element comprising: a duct; three planar electrode means in said duct, said electrode means being perpendicular to the axis from said duct and spaced from each other, whereby a first electrode means is disposed between the other two electrode means, each of said electrode means comprising a frame including two spaced and parallel bars of conducting material, a plurality of conductor engaging means fixed at regular intervals along said bars, a length of braided wire conductor laced on said engaging means to form an array of parallel conductors extending between said bars, the engaging means of the frame of said first electrode means being positioned with respect to the engaging means of the frame of at least one other of the planar electrode means so that their respective conductors are mutually offset with respect to the axis of said duct; means for applying a first voltage which sinusoidally varies about ground potential to said said first electrode means; and means for applying a second voltage which is unidirectional with respect to ground potential and has a substantially sawtooth waveform with a portion thereof having an AC.

ripple to both of said other two electrode means. 

1. An electrostatic gas filter element to be positioned upstream of a collector element comprising: a duct; three planar electrode means in said duct, said electrode means being perpendicular to the axis from said duct and spaced from each other, whereby a first electrode means is disposed between the other two electrode means, each of said electrode means comprising a frame including two spaced and parallel bars of conducting material, and a length of braided multi-wire metallic conductor connected to said parallel bars to form an array of parallel conductors extending between said bars, the parallel conductors of said first electrode means being positioned with respect to the parallel conductors of at least one other of the planar electrode means so as to be mutually offset with respect to the axis of said duct; means for applying a first voltage which sinusoidally varies about ground potential to said said first electrode means; and means for applying a second pulsating voltage which is unidirectional with respect to ground potential with a portion of its waveform having an A.C. ripple to both of said other two electrode means.
 2. The electrostatic gas filter element of claim 1 wherein each of said two spaced and parallel bars carry a plurality of spacers and said length of multiwire metallic conductor is alternately and regularly wrapped in gaps between said spacers and extending across the space between said bars.
 3. The electrostatic gas filter element of claim 1 wherein said second voltage has an amplitude in the kilovolt range.
 4. The electrostatic gas filter element of claim 1 wherein the wires of said metalliC conductor are braided according to a diamond pattern.
 5. An electrostatic gas filter element to be positioned upstream of a collector element comprising: a duct; three planar electrode means in said duct, said electrode means being perpendicular to the axis from said duct and spaced from each other, whereby a first electrode means is disposed between the other two electrode means, each of said electrode means comprising a frame including two spaced and parallel bars of conducting material, a plurality of conductor engaging means fixed at regular intervals along said bars, a length of braided wire conductor laced on said engaging means to form an array of parallel conductors extending between said bars, the engaging means of the frame of said first electrode means being positioned with respect to the engaging means of the frame of at least one other of the planar electrode means so that their respective conductors are mutually offset with respect to the axis of said duct; means for applying a first voltage which sinusoidally varies about ground potential to said said first electrode means; and means for applying a second voltage which is unidirectional with respect to ground potential and has a substantially sawtooth waveform with a portion thereof having an A.C. ripple to both of said other two electrode means. 